The present invention relates to the structure of an ignition coil to supply the high voltage to an ignition plug.
For the ignition coil used in the recent internal combustion engine for the automobile, there is a conflicting requirement which is the downsizing and the increasing of the output for corresponding to a lean-burn engine considering about the global atmosphere.
Among them, the ignition coil to directly supply the high voltage to the ignition plug, has advantages that the space above the engine head can be reduced because the a portion or an almost portion of the ignition coil is accommodated in a plug hole of the engine head, the generation of the noise at the time of the ignition which has a bad influence on the electrical equipments, is small because the high voltage is directly supplied to the ignition plug and a wire to transmit the high voltage to the ignition plug such as a high tension cable to directly supply the high voltage to the ignition plug, is not necessary, and the transmission loss of the ignition energy to the ignition plug is small, and therefore, it is used for many engines.
A longitudinal sectional view showing the conventional ignition coil to directly supply the high voltage to the ignition plug is shown in FIG. 4. Conventionally, in an upper accommodation portion 11b of a case 11 of the ignition coil to directly supply the high voltage to the ignition plug, a primary voltage input portion 12, or depending on the case, an igniter 13 to turn on-off the primary current is accommodated, and inside the case 11, a central iron core 18 on which magnets 21 to generate the magnetic flux in the direction reverse to the magnetic flux generated in a primary coil 15 in order to suppress the saturation of the magnetic flux of the iron core, are mounted, on its both ends, is accommodated, and a secondary coil 17 in which a secondary copper wire is wound around a secondary bobbin 16, a primary coil 15 in which a primary copper wire is wound around a primary bobbin 14, and a sheath iron core 19 which is formed into the cylindrical-shape, and has a cutout portion on a portion of its circular periphery, are arranged in their order, coaxially with the central iron core 18, and a secondary high voltage terminal 22 is provided on the bottom portion of the case 11, and the secondary high voltage terminal 22 is electrically connected to the secondary coil and a spring 23 in a high voltage tower portion 11a provided in the case 11, and from the opening portion of the upper portion of the case 11, epoxy resin is filled in the case, hardened, and the case is sealed in the insulation. Further, in the high voltage tower portion 11a, a protector 25 is provided so that the high voltage does not leak to a metallic portion such as a plug hole, not shown, and at the time of operation of the ignition coil, the primary current is inputted from the primary voltage input portion 12, and it flows to the primary coil 15, and the magnetic energy generated in the primary coil 15 is transmitted through the central iron core 18 and the sheath iron core 19, and the high voltage corresponding to the winding ratio of the primary coil 15 and the secondary coil 17 is generated in the secondary coil 17. The generated high voltage passes through the secondary high voltage terminal 22 from the secondary coil, and through the spring 23, it is sent to the ignition plug, not shown, connected to the spring 23.
However, in the conventional technology, as shown in FIG. 5, because the secondary coil 17 coaxially arranged with the central iron core 18 in the case 11, is housed in the primary coil 15 coaxially arranged in the same manner, and the insulation of the high voltage output side of the secondary coil 17 is made by filling and hardening the insulation material such as epoxy resins, the epoxy resin is peeled from each of members by the aging thermal stress, and specifically when the primary bobbin 14 is peeled in the vicinity of the high voltage portion of the secondary coil 17, the high voltage generated in the secondary coil 17 leaks in the space formed by the peeling, and the high voltage is short-circuited to the low voltage portion such as the primary coil 15 in such a manner that the high voltage creeps along the surface of the member, and it causes the disadvantage which results in the dielectric breakdown.
Further, as the ignition coil to generate the high voltage energy, there are methods in which the winding number of the primary coil 15 and the secondary coil 17 is kept as it is, and the diameter of the wound coil is increased, and the electric resistance of these coils is reduced, or the outer shape of the coil is increased in such a manner that the sectional area of the iron core is increased and the efficiency of the magnetic circuit is increased, however, for the cylindrical type ignition coil which is a type to be housed in the plug hole whose diameter is generally called to be about 20 to 35 mm, and in which the restriction of the dimensions is severe, it is difficult that the primary coil 15, secondary coil 17, central iron core 18, sheath iron core 19, and igniter 13 are housed in the case 11, and the above method is adopted.
Further, even when the ignition coil is not the type which is housed in the plug hole, there is a requirement of the size and weight reduction for the ignition coil, from points of attachment property, oscillation property, and consumption energy.
Accordingly, the object of the present invention is to solve the above problems and to provide a long life and small sized ignition coil.
In order to attain the above object, the structure of the ignition coil to directly supply the high voltage to the ignition plug, is changed from the conventional one. The ignition coil of the present invention is an ignition coil which is characterized in that: the central iron core, and the secondary coil in which the secondary copper wire is coaxially wound around the central iron core, are housed in the case, and the primary coil in which the primary copper wire is wound around the outside of the case, coaxially with the central iron core in the same manner, and the sheath iron core is arranged outside these central iron core, secondary coil, case and primary coil.
Further, the ignition coil of the present invention may also be an ignition coil which is characterized in that the heat resistive insulation material is wound to protect the primary coil, and the heat resistive insulation material is wound, and further, it may be characterized in that the heat resistive insulation material is mounted on the outside of sheath iron core of the ignition coil, and as the heat resistive insulation material, the insulation tape, heat contraction tube, fluoric-rubber, or silicon may be used.
When the above solving means is used, the disadvantage in which the secondary output high voltage flows and leaks in the primary coil 15 in the vicinity of the peeled portion, in the epoxy resin peeling from the primary bobbin 14 and the secondary bobbin 16 inside the case 11 by the aging deterioration of the conventional ignition coil, is not generated because the secondary coil 17 and the primary coil 15 are partitioned from each other, when the secondary coil 17 is housed in the case 11, and the primary winding is wound around the outside of the case.
Further, when the primary bobbin portion 14a is provided in the case 11, the wall thickness portion of the conventional primary bobbin 14 is abolished, and in its space portion, the diameter of the winding can be increased, or the sectional area of the sheath iron core 19 can be increased, and the secondary output energy can be increased, and when the diameter of the winding or the sectional area of the sheath iron core 19 is the same as the conventional one, the outer shape of the ignition coil can be reduced to the smaller one by the amount of the wall thickness of the primary bobbin 14.